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what does a dependent power supply look like?!

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PG1995

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Hi :)

I was wondering what a dependent power supply, either voltage or current, looks like. I have seen a 'general' power supply in the lab (see link #2). Actually I was looking at the example problem 1.7 in the given link #1. It has a dependent current which is rated 0.2I. When I is 5A, the current supply by the dependent source is 1A. But how does it sense that the current supplied by the "independent" source on the left is 5A. There should be some way; I don't think it works using telepathic means!;)

Please help me. Thanks a lot.

1: example problem from the book:
https://img716.imageshack.us/img716/2527/dependentsupply.jpg

2: the power supply I've seen in the lab:
**broken link removed**
 
I've never heard of a "dependent" power supply, though I'm no expert. It may be something of an academic construct for the sake of a textbook example, or it may be a real thing.

If it's a real thing, then you're correct in saying tht it can't work by telepathy. There must be an input to the power supply that tells it what the independent current is, such as a voltage read across a current-sensing resistor.
 
You can have MASTER/SLAVE power supplies and TRACKING power supplies and PROGRAMMABLE power supplies. In the later case a voltage e.g. 0-10 V represents, 0- full scale output.

. You need the dependent supplies to analize simple circuits. A transistor, for instance.
 
The linearity of the dependent supply is the key to such measurements... Nothing more than an abstract from the real world to define what is required to realize the results that are found in the theoretical world.
 
The linearity of the dependent supply is the key to such measurements... Nothing more than an abstract from the real world to define what is required to realize the results that are found in the theoretical world.

Hi Sceadwian

Could you please explain your reply a bit so I could understand it? Thank you.
 
I'd like to know as well. To be honest, I don't think it's a very good explanation.

According to the O.P.'s textbook, a dependent power supply is one whose output (current in this case) depends on a condition elsewhere in a circuit. In this case, the example is 0.2I, where I is (presumably) a current somewhere else in the circuit. So how does that work?

And is a dependent power supply, such as described here, something you can pick up at an electronics supplier? or is it just an abstract concept used in teaching electronics? (I suspect the latter.)

Not sure either about the comment above that "all real-world supplies are dependent". Not in the way described here, where current is a fixed fraction of another current.
 
I'd like to know as well. To be honest, I don't think it's a very good explanation.

According to the O.P.'s textbook, a dependent power supply is one whose output (current in this case) depends on a condition elsewhere in a circuit. In this case, the example is 0.2I, where I is (presumably) a current somewhere else in the circuit. So how does that work?

And is a dependent power supply, such as described here, something you can pick up at an electronics supplier? or is it just an abstract concept used in teaching electronics? (I suspect the latter.)

Not sure either about the comment above that "all real-world supplies are dependent". Not in the way described here, where current is a fixed fraction of another current.

carbonzit: I'm happy you understand my question well.
 
Hi :)

I was wondering what a dependent power supply, either voltage or current, looks like. I have seen a 'general' power supply in the lab (see link #2). Actually I was looking at the example problem 1.7 in the given link #1. It has a dependent current which is rated 0.2I. When I is 5A, the current supply by the dependent source is 1A. But how does it sense that the current supplied by the "independent" source on the left is 5A. There should be some way; I don't think it works using telepathic means!;)

Please help me. Thanks a lot.

1: example problem from the book:
https://img716.imageshack.us/img716/2527/dependentsupply.jpg

2: the power supply I've seen in the lab:
**broken link removed**


Hi,


Some very good questions. It's not obvious sometimes when you first look at these dependent sources (that's really what they are called), but if you look close at the circuit in the first link, you will see one of the connecting lines (usually taken to be perfect wires) labeled with "I=5A". Then if you look at the dependent source you will see it is labeled "0.2I" which really means "0.2*I" (ie 0.2 times I). Now we know where I is located (it's in the line labeled "I=5A" or sometimes just "I", so we take I and multiply it by 0.2 and that's how we get the current of the dependent source. In this case I=5 so that means the dependent source has 0.2*5 which equals 1 amp flowing through it.
The reason this seems strange is probably because there is no indication what the 0.2I source is 'sensing', but it is implied by the "0.2I" part. Sometimes there are lines drawn and an arrow to show current direction of the sense leads too, but many times there are no lines drawn for the sensing part of the dependent source, just a label. It means that the dependent source is sort of 'measuring' that other place in the circuit and using that to determine its own current or voltage.

Another example: Say we see "6*Ix" next to a dependent current source. We would then look for where "Ix" is in the circuit and that's what we would use to calculate the current from the dependent current source. If we found Ix was equal to 1 amp then the dependent current would be 6 times that.
Another: Say we see "8*Vx" next to a dependent current source. We would then look for where "Vx" is in the circuit and use that to find the unknown current.
Another: Say we see "8*Vx" next to a dependent voltage source. We would then look for where "Vx" is in the circuit and use that to find the unknown voltage of the dependent voltage source.

So we have several types of dependent sources:
Voltage controlled voltage source,
Current controlled voltage source,
Voltage controlled current source, and
Current controlled current source.

In real life others have mentioned the kinds of real power supplies available. Also in real life however the dependent current and voltage sources are used as part of sub circuits to show how some real life circuit would work. For example, a real life op amp can be made using a dependent voltage or current source, and this kind of sub circuit would have many qualities similar to a real life op amp.
 
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I was not trying to be flip or attempting to confuse. The original question set off a chain reaction in my thinking and I commented on the nature of supplies rather then answering your question.

Just the same it would be good if you could understand the following.

All real world supplies are dependent because their output depends on other parameters within a circuit. Look at the datasheet for a regulator or a battery, there are graphs involving current, voltage and temperature. These indicate dependencies. The independent power supply is a convenient but untrue generalization we can use if we keep our demands within the normal operational range of the supply.

My apologies.
 
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